1. Field of the Invention
This invention relates to burner heaters where a fluid fuel is continuously injected and burned in a combustion chamber and the hot combustion gases are passed through a heat exchanger for heating a fluid. More particularly, the invention is directed to various devices and methods for controlling and suppressing in certain of such burners the onset of an undesirable acoustical phenomenon, referred to as buzzing in this disclosure.
2. State of the Prior Art
Direct fired heaters have long been used in such applications as aircraft deicers for heating large quantities of deicing solution, for rapidly vaporizing liquid nitrogen in industrial installations and oil wells, and for heating water.
This applicant has developed heaters of this type which are characterized by compact burner size, as measured by volume of the combustion chamber, in relation to the BTU capacity of the burner, typically several million BTU/Hour and ranging as high as 12 million BTU/Hour, at heat rates of 1 to 2 million BTU/Hour/Cubic Ft.. The high BTU capacity in these burners is the result of a swirling of the air input to the burner. This creates intense mixing within the combustion flame. This is in contrast to the burner designs of other manufacturers where the flame follows a generally straight path towards the discharge end of the combustion chamber, resulting in less intense combustion so that less fuel can be burned for a given combustion chamber volume.
The general configuration of applicant's direct fired heaters is disclosed in U.S. Pat. Nos. 4,373,896 and 4,374,637. It includes an inner barrel combustion chamber with a fuel block at a closed end of the barrel, an outer barrel coaxially surrounding the inner barrel and defining an annular space between the two barrels, and a blower mounted for driving a stream of air through this annular space and into the inner barrel through inlet openings in the back wall and in the cylindrical wall of the combustion chamber. The closed end of the combustion chamber is normally squared, i.e., it is closed by a generally planar back wall perpendicular to the barrel axis. The fuel block is centered in the back wall and includes a number of fuel injectors which spray finely dispersed fuel towards the periphery of the chamber, and an ignition unit which is typically a spark plug for initiating combustion of the fuel. The back wall has air inlets and swirling vanes which direct the inlet air stream such that the flame produced by the burning air-fuel mixture follows a generally helicoidal path bout the barrel axis and against the cylindrical wall of the chamber as it travels towards the opposite, open end of the chamber. Bypass holes are formed on the cylindrical wall of the inner barrel downstream of the backwall to admit additional air from the air stream flowing in the annular space between the two barrels in order to reduce discharge temperature. The outer barrel is closed at both ends and there is an exhaust stack for venting the combustion gases to the atmosphere. The exhaust stack may be at a right angle to the axis of the two barrels. Combustion gases flow through a heat exchanger for heating a fluid medium circulating through the heat exchanger interposed between the open end of the combustion chamber and the exhaust stack.
Under some operating conditions, particularly when burning gaseous or highly volatile liquid fuels such as gasoline, an undesirable acoustically coupled combustion instability can arise. This acoustically coupled combustion instability called buzzing can generate intense sounds which may be unacceptable in many applications. This applicant is not aware of existing solutions for controlling the onset of buzzing in burners of the aforedescribed type. A solution to this problem is needed.